1. Field of the Invention
This invention is suitable for an image display apparatus, and for example, a head mounted display (hereinafter referred to as HMD) or the like designed to enlarge and observe image information displayed on a reflection type liquid crystal display element through an optical element having a free curved surface appropriately set.
2. Related Background Art
There have heretofore been proposed various head mounted type image observation apparatuses, i.e., so-called HMDs using, for example, an optical element provided with an incident surface and a plurality of reflecting surfaces on the surface of a transparent member to enable image information displayed on an image display element such as liquid crystal to be observed as an enlarged virtual image.
Such HMD type image observation apparatuses are proposed, for example, in Japanese Laid-Open Patent Application No. 7-333551, Japanese Laid-Open Patent Application No. 8-179238, Japanese Laid-Open Patent Application No. 8-234137, etc.
Also, there have been proposed various HMDs using, for example, an optical system comprising a plurality of mirrors eccentrically disposed to enable image information displayed on an image display element such as liquid crystal to be observed as an enlarged virtual image. Such HMD type image observation apparatuses are proposed, for example, in Japanese Laid-Open Patent Application No. 7-191274, Japanese Laid-Open Patent Application No. 8-286140, etc.
On the other hand, in recent years, various reflection type liquid crystal display elements have been used as compact display devices. To use a reflection type liquid crystal display element in an image observation apparatus such as HMD, it is necessary to provide an illuminating device and illuminate the liquid crystal display element.
FIGS. 17 and 18 of the accompanying drawings are schematic views of essential portions of image display apparatuses using reflection type liquid crystal display elements according to the prior art.
In FIG. 17, reference numeral 101 designates a. reflection type liquid crystal display element which is illuminated by a light beam from a light source 102 through a half mirror 103. When the apparatus is a projection, image information subjected to light modulation by the liquid crystal display element 101 is projected onto a predetermined surface by a projection lens 104 through the half mirror 103 and is observed. Also, when the apparatus is an HMD, image information displayed by the liquid crystal display element 101 through the lens system 104 is enlarged and observed.
In FIG. 18, a light beam from a light source 102 is made into linearly polarized light (e.g. P-polarized light) through a polarizing plate 106, and is passed through a polarizing beam splitter 105 and illuminates a reflection type liquid crystal display element 101. The light beam (now S-polarized light) subjected to light modulation by the liquid crystal display element 101 is reflected by the polarizing beam splitter 105 and is directed to a projection lens or a lens system 104.
Thereby, when the apparatus is a projector, the light beam is projected onto a predetermined surface by the projection lens 104 and is observed. Also, when the apparatus is an HMD, image information displayed by the liquid crystal display element 101 through the lens system 104 is enlarged and observed.
When a reflection type liquid crystal display element is used as an image display apparatus, it is necessary to incorporate an illuminating device for illuminating it into the apparatus.
When a reflection type liquid crystal display element is used as image display means, it is necessary to incorporate an illuminating device for illuminating it into the optical path of a display optical system, and this has led to the problem that as compared with a case where a transmission type liquid crystal display element or the like is used, the difficulty in designing increases and a reduction in the specification of the angle of view, eye relief or the like is caused.
When the image display apparatus is used for an HMD, it is desired that the entire apparatus be as compact and light in weight as possible to enable it to be mounted on an observer's head.